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United States Patent |
5,023,009
|
Merchant
|
June 11, 1991
|
Binary azeotropic compositions of
1,1,1,2,3,3-hexafluoro-3-methoxypropane and
2,2,3,3,3-pentafluoropropanol-1
Abstract
The azeotropic mixture of 1,1,1,2,3,3-hexafluoro-3-methoxypropane and
2,2,3,3,3-pentafluoropropanol-1, and the use of such azeotropic mixture
as: a cleaning agent, a blowing agent, a refrigerant, an aerosol
propellant, a heat transfer medium, a fire extinguishing agent, a gaseous
dielectric and a power cycle working fluid is disclosed.
Inventors:
|
Merchant; Abid N. (Wilmington, DE)
|
Assignee:
|
E. I. Du Pont de Nemours and Company (Wilmington, DE)
|
Appl. No.:
|
592562 |
Filed:
|
October 3, 1990 |
Current U.S. Class: |
252/67; 62/114; 134/12; 134/38; 134/39; 134/40; 203/67; 252/69; 252/364; 510/177; 510/180; 510/243; 510/244; 510/273; 521/98; 521/131 |
Intern'l Class: |
C11D 007/30; C11D 007/50; C23G 005/028; C09K 005/04 |
Field of Search: |
252/62,170,171,172,305,364,67,69,DIG. 9
203/67
134/12,38,39,40
521/98,131
62/114
|
References Cited
U.S. Patent Documents
2795601 | Jun., 1957 | Rendall et al. | 560/219.
|
2862024 | Nov., 1958 | Rendall et al. | 560/227.
|
2999815 | Sep., 1961 | Eiseman, Jr. | 252/171.
|
2999817 | Sep., 1961 | Bower | 252/172.
|
3291844 | Dec., 1966 | Watson | 568/685.
|
3691092 | Sep., 1972 | Floria | 252/364.
|
3881949 | May., 1975 | Brock | 134/31.
|
3903009 | Sep., 1975 | Bauer et al. | 252/171.
|
4357282 | Nov., 1982 | Anderson et al. | 568/676.
|
4482465 | Nov., 1984 | Gray | 252/67.
|
Foreign Patent Documents |
62-260899 | Nov., 1987 | JP.
| |
Primary Examiner: Clingman; A. Lionel
Assistant Examiner: Skaling; Linda D.
Attorney, Agent or Firm: Shipley; James E.
Claims
We claim:
1. An azeotropic composition consisting essentially of about 95-99 weight
percent 1,1,1,2,3,3-hexafluoro-3-methoxypropane and about 1-5 weight
percent 2,2,3,3,3-pentafluoropropanol-1, wherein the composition has a
boiling point of about 54.4.degree. C. when the pressure is adjusted to
substantially atmospheric pressure.
2. An azeotropic composition of claim 1, consisting essentially of about
97.0 weight percent 1,1,1,2,3,3-hexafluoro-3-methoxypropane and about 3.0
weight percent 2,2,3,3,3-pentafluoropropanol-1.
3. A process for cleaning a solid surface which comprises treating said
surface with an azeotropic composition of claim 1.
4. A process of claim 3, wherein the solid surface is a printed circuit
board contaminated with flux and flux-residues.
5. A process of claim 4, wherein the solid surface is a metal, a glass or a
plastic.
6. A process for preparing a polymer foam comprising expanding a polymer
with a blowing agent, the improvement wherein the blowing agent is an
azeotropic composition of claim 1.
7. A process for producing refrigeration which comprises evaporating an
azeotropic composition of claim 1 in the vicinity of a body to be cooled.
8. A process for producing heat which comprises condensing an azeotropic
composition of claim 1 in the vicinity of a body to be heated.
Description
FIELD OF THE INVENTION
The present invention relates to binary azeotropic compositions of
1,1,1,2,3,3-hexafluoro-3-methoxypropane and
2,2,3,3,3-pentafluoropropanol-1 and the use of such azeotropic
compositions as a cleaning solvent, blowing agent, refrigerant, heat
transfer media, aerosol propellant, or power cycle working fluid.
BACKGROUND OF THE INVENTION
As modern electronic circuit boards evolve toward increased circuit and
component densities, thorough board cleaning after soldering becomes a
more important criterion. Current industrial processes for soldering
electronic components to circuit boards involve coating the entire circuit
side of the board with flux and thereafter passing the flux-coated board
over preheaters and through molten solder. The flux cleans the conductive
metal parts and promotes solder fusion. Commonly used solder fluxes
generally consist of rosin, either used alone or with activating
additives, such as amine hydrochlorides or oxalic acid derivatives.
After soldering, which thermally degrades part of the rosin, the
flux-residues are often removed from the circuit boards with an organic
solvent. The requirements for such solvents are very stringent. Defluxing
solvents should have the following characteristics: a low boiling point,
be nonflammable, have low toxicity and have high solvency power, so that
flux and flux-residues can be removed without damaging the substrate being
cleaned.
While boiling point, flammability and solvent power characteristics can
often be adjusted by preparing solvent mixtures, these mixtures are often
unsatisfactory because they fractionate to an undesirable degree during
use. Such solvent mixtures also fractionate during solvent distillation,
which makes it virtually impossible to recover a solvent mixture with the
original composition.
On the other hand, azeotropic mixtures, with their constant boiling points
and constant compositions, have been found to be very useful for these
applications. Azeotropic mixtures exhibit either a maximum or minimum
boiling point and they do not fractionate on boiling. These
characteristics are also important when using solvent compositions to
remove solder fluxes and flux-residues from printed circuit boards.
Preferential evaporation of the more volatile solvent mixture components
would occur, if the mixtures were not azeotropic and would result in
mixtures with changed compositions, and with attendant less-desirable
solvency properties, such as lower rosin flux solvency and lower inertness
toward the electrical components being cleaned. The azeotropic character
is also desirable in vapor degreasing operations, where redistilled
solvent is generally employed for final rinse cleaning.
In summary, vapor defluxing and degreasing systems act as a still. Unless
the solvent composition exhibits a constant boiling point, i.e., is
azeotropic, fractionation will occur and undesirable solvent distributions
will result, which could detrimentally affect the safety and efficacy of
the cleaning operation.
A number of chlorofluorocarbon based azeotropic compositions have been
discovered and in some cases used as solvents for solder flux and
flux-residue removal from printed circuit boards and also for
miscellaneous degreasing applications. For example: U.S. Pat. No.
3,903,009 discloses the ternary azeotrope of
1,1,2-trichlorotrifluoroethane with ethanol and nitromethane; U.S. Pat.
No. 2,999,815 discloses the binary azeotrope of
1,1,2-trichlorotrifluoroethane and acetone; U.S. Pat. No. 2,999,817
discloses the binary azeotrope of 1,1,2-trichlorotrifluoroethane and
methylene chloride.
Such mixtures are also useful as buffing abrasive detergents, for the
removal of buffing abrasive components from polished surfaces, as drying
agents for cleaned polished surfaces such as jewelry and metals and as
resist-developers in conventional circuit manufacturing techniques, which
employ chlorine-type developing agents. The mixtures are also useful as
refrigerants, heat transfer media, gaseous dielectrics, foam expansion
agents, aerosol propellants, solvents, power cycle working fluids and fire
extinguishing agents. Further, in many cases, the halocarbon components of
the azeotropic mixtures &themselves, would be effective in these
applications.
Closed-cell polyurethane foams are widely used for insulation purposes in
building construction and in the manufacture of energy efficient
electrical appliances. Polyisocyanurate board stock is used by the
construction industry, in roofing and siding for both its insulative and
load-carrying capabilities. Sprayed polyurethane foams are also used in
construction for the insulation of large structures such as storage tanks.
Pour-in-place polyurethane foams are used as insulative barriers in
appliances such as refrigerators and freezers and also in much larger
items such as trailer and railroad tanks.
All of the aforementioned types of expandable foam require the use of
expansion agents (blowing agents) for their manufacture. Insulative foams
require the use of halocarbon blowing agents, owing to their low vapor
thermal conductivities, not only to expand the polymer but also to impart
an essential insulation feature to the expanded foam. Historically,
polyurethane and polyisocyanurate foams have been produced using
trichlorofluoromethane (CFC-11), as the blowing agent of choice.
Another important type of insulative foam is the phenolic foam. These foams
have heretofore generally been expanded with blends of
trichlorofluoromethane (CFC-11) and 1,1,2-trichlorotrifluoroethane
(CFC-113) blowing agents.
Still another insulating foam is the thermoplastic or polyolefin type foam.
These are generally the polyethylene and polypropylene foams, used widely
in packaging. Thermoplastic foams are usually expanded with
dichlorodifluoromethane (CFC-12).
Many smaller scale hermetically sealed, refrigeration systems, such as
those used in refrigerators or window and auto air conditioners, use
dichlorodifluoromethane (CFC-12) as the refrigerant. Larger scale
centrifugal refrigeration equipment, such as those used for industrial
scale cooling, e.g, commercial office buildings, generally employ
trichlorofluoromethane (CFC-11) or 1,1,2-trichlorotrifluoroethane
(CFC-113) as the refrigerants of choice. Azeotropic mixtures, with their
constant boiling points and compositions have also been found to be very
useful as substitute refrigerants, for the applications cited above.
Aerosol products have employed both individual halocarbons and halocarbon
blends as propellant systems. Halocarbons have also been used both as
solvents and propellant vapor pressure attenuators, in aerosol systems.
Azeotropic mixtures, with their constant compositions and vapor pressures
would be very useful as solvents and propellants in aerosol systems.
Some of the chlorofluorocarbons which are currently used as cleaning
agents, blowing agents, refrigerants, aerosol propellants and for other
applications, have been linked, theoretically, to depletion of the earth's
protective ozone layer. As early as the mid-1970's, it was known that
introduction of hydrogen atoms into the chemical structure of previously
fully-halogenated chlorofluorocarbons would reduce the chemical stability
of these compounds. Hence, the now destabilized compounds would be
expected to degrade in the lower atmosphere and not reach the
stratospheric ozone layer in-tact. What is also needed, therefore, are
substitute halocarbons, which have low theoretical ozone depletion
potentials.
Unfortunately, as recognized in the art, it is not possible to predict the
formation of azeotropes. This fact complicates the search for new
azeotropic compositions, which have application in the field.
Nevertheless, there is a constant effort in the art to discover new
azeotropic compositions, which have desirable end-use characteristics.
SUMMARY OF THE INVENTION
According to the present invention, binary, azeotropic compositions have
been discovered comprising admixtures of effective amounts of
1,1,1,2,3,3-hexafluoro-3-methoxypropane and
2,2,3,3,3-pentafluoropropanol-1. The azeotrope is an admixture of about
95-99 weight percent 1,1,1,2,3,3-hexafluoro-3-methoxypropane and about 1-5
weight percent 2,2,3,3,3-pentafluoropropanol-1. The present invention
provides minimum-boiling, azeotropic compositions which are useful as
cleaning agents, blowing agents, refrigerants, aerosol propellants, heat
transfer media, fire extinguishing agents, gaseous dielectrics, and power
cycle working fluids. These blends are potentially environmentally safe
substitutes for the halocarbons now used in the applications described
above.
DETAILED DESCRIPTION OF THE INVENTION
The composition of the instant invention comprises an admixture of
effective amounts of 1,1,1,2,3,3-hexafluoro-3-methoxypropane (CF.sub.3
--CHF--CF.sub.2 --O--CH.sub.2 --CH.sub.2 --CH.sub.3, boiling point
=54.0.degree. C. and 2,2,3,3,3-pentafluoropropanol-1 (CF.sub.3 --CF.sub.2
--CH.sub.2 OH, boiling point=80.degree. C., at 748 mm Hg) to form the
minimum-boiling, azeotropic composition.
By azeotropic composition is meant, a constant boiling liquid admixture of
two or more substances, whose admixture behaves as a single substance, in
that the vapor, produced by partial evaporation or distillation of the
liquid has the same composition as the liquid, i.e., the admixture
distills without substantial composition change. Constant boiling
compositions, which are characterized as azeotropic, exhibit either a
maximum or minimum boiling point, as compared with that of the
nonazeotropic mixtures of the same substances.
By effective amount is meant the amount of each component of the instant
invention admixture, which when combined, results in the formation of the
azeotropic composition of the instant invention.
It is possible to fingerprint, in effect, a constant boiling admixture,
which may appear under many guises, depending upon the conditions chosen,
by any of several criteria:
The composition can be defined as an azeotrope of A and B, since the very
term "azeotrope" is at once both definitive and limitative, and requires
that effective amounts of A and B form this unique composition of matter,
which is a constant boiling admixture.
It is well known by those skilled in the art that at different pressures,
the composition of a given azeotrope will vary--at least to some
degree--and changes in pressure will also change--at least to some
degree--the boiling point temperature. Thus an azeotrope of A and B
represents a unique type of relationship but with a variable composition
which depends on temperature and/or pressure. Therefore compositional
ranges, rather than fixed compositions, are often used to define
azeotropes.
The composition can be defined as a particular weight percent relationship
or mole percent relationship of A and B, while recognizing that such
specific values point out only one particular such relationship and that
in actuality, a series of such relationships, represented by A and B
actually exist for a given azeotrope, varied by the influence of pressure.
Azeotrope A and B can be characterized by defining the composition as an
azeotrope characterized by a boiling point at a given pressure, thus
giving identifying characteristics without unduly limiting the scope of
the invention by a specific numerical composition, which is limited by and
is only as accurate as the analytical equipment available.
Binary mixtures of about 95-99 weight percent
1,1,1,2,3,3-hexafluoro-3-methoxypropane and about 1-5 weight percent
2,2,3,3,3-pentafluoropropanol-1 are characterized as azeotropic, in that
mixtures within this range exhibit a substantially constant boiling point
at constant pressure. Being substantially constant boiling, the mixtures
do not tend to fractionate to any great extent upon evaporation. After
evaporation, only a small difference exists between the composition of the
vapor and the composition of the initial liquid phase. This difference is
such that the compositions of the vapor and liquid phases are considered
substantially identical. Accordingly, any mixture within this range
exhibits properties which are characteristic of a true binary azeotrope.
The binary composition which consists of about 97.0 weight percent
1,1,1,2,3,3-hexafluoro-3-methoxypropane and about 3.0 weight percent
2,2,3,3,3-pentafluoropropanol-1 has been established, within the accuracy
of the fractional distillation method, as a true binary azeotrope, boiling
at about 54.4.degree. C., at substantially atmospheric pressure.
The aforestated azeotrope has a low ozone-depletion potential and is
expected to decompose almost completely, prior to reaching the
stratosphere.
The azeotropic composition of the instant invention permits easy recovery
and reuse of the solvent from vapor defluxing and degreasing operations
and/or refrigeration operations, because of its azeotropic nature.
The azeotrope of this invention can be used in cleaning processes such as
described in U.S. Pat. No. 3,881,949, which is incorporated hereon by
reference.
The language "consisting essentially of"
1,1,1,2,3,3-hexafluoro-3-methoxypropane and
2,2,3,3,3-pentafluoropropanol-1 is not intended to exculed the presence of
minor amounts of other materials which do not significantly alter the
azeotropic character of the composition.
The azeotropic composition of the instant invention can be prepared by any
convenient method including mixing or combining the desired component
amounts. A preferred method is to weigh the desired component amounts and
thereafter combine them in an appropriate container.
The entire disclosure of all applications, patents and publications, cited
above and below, are hereby incorporated by reference.
EXAMPLE 1
A solution which contained 92.7 weight percent
1,1,1,2,3,3-hexafluoro-3-methoxypropane and 7.3 weight percent
2,2,3,3,3-pentafluoropropanol-1 was prepared in a suitable container and
mixed thoroughly.
The solution was distilled in a 5 plate Oldershaw distillation column,
using about a 10:1 reflux to take-off ratio. Head temperatures were read
directly to 0.1.degree. C. All temperatures were adjusted to 760 mm
pressure. Distillate compositions were determined by gas chromatography.
Results obtained are summarized in Table 1.
TABLE 1
______________________________________
DISTILLATION OF:
(92.7 + 7.3)
1,1,1,2,3,3-HEXAFLUORO-3-METHOXYPROPANE (HFMEP),
AND 2,2,3,3,3-PENTAFLUOROPROPANOL-1 (PEFP)
WT %
DISTILLED
HEAD OR PERCENTAGES
CUTS TEMP., .degree.C.
RECOVERED HFMEP PEFP
______________________________________
PRE 54.3 9.1 97.41 2.59
1 54.3 19.6 97.45 2.55
2 54.3 28.1 97.31 2.69
3 54.2 36.2 97.25 2.75
4 54.5 45.0 96.90 3.10
5 54.5 52.7 96.81 3.19
6 54.5 61.0 96.30 3.70
HEEL -- 82.4 86.98 13.02
______________________________________
Analysis of the above data indicates very small differences exist between
head temperatures and distillate compositions, as the distillation
progressed. A statistical analysis of the data demonstrates that the true
binary azeotrope of 1,1,1,2,3,3-hexafluoro-3-methoxypropane and
2,2,3,3,3-pentafluoropropanol-1 has the following characteristics at
atmospheric pressure (99 percent confidence limits):
1,1,1,2,3,3-Hexafluoro-3-methoxypropane=97.0.+-.0.3 wt. %
2,2,3,3,3-Pentafluoropropanol-1=3.0.+-.0.3 wt. %
boiling point, .degree.C.=54.4.+-.0.1
EXAMPLE 2
Several single sided circuit boards were coated with activated rosin flux
and soldered by passing the boards over a preheater, to obtain top side
board temperatures of approximate 200.degree. F. (93.degree. C.), and then
through 500.degree. F. (260.degree. C.) molten solder. The soldered boards
were defluxed separately, with the axeotropic mixture cited in Example 1
above, by suspending a circuit board, first, for three minutes in the
boiling sump, which contained the azeotropic mixture, then, for one minute
in the rinse sump, which contained the same azeotropic mixture, and
finally, for one minute in the solvent vapor above the boiling sump. The
boards cleaned in the azeotropic mixture had no visible residue remaining
thereon.
From the foregoing description, one skilled in the art can easily ascertain
the essential characteristics of this invention, and without departing
from the spirit and scope thereof, can change and modify the invention to
adapt it to various usages and conditions.
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